Really long seatpost?

I just got a BMX bike today to convert to a mini-velo. First I want to get a seatpost that's long enough. Looking around, I found I can get a FSA 27.2x420mm seatpost for $25. With that and my Velo Webspring saddle, I think it will be enough, but I'm not sure. To get that one to fit, I'd need a shim, as the original is 28.6mm. Is it possible to use the shim in a way to extend it more? If not, anything else I can use to get a bit more length? Should I just find a pipe at the hardware store that will fit instead?

I'm not too concerned with the looks, but I think it could be counted as one. Along with the seatpost, I'm planning on an IGH, fenders, and maybe different handlebars and a rack.

I looked at folding bike stuff, and it seems like the only things that will work only come with a bike and can't be bought separate.

IGH?....no. won't really work. You're looking at a new (bigger) crank to make the gear ratios high enough to work. Then you have chainline issues with that. You also don't have any cable stops on a BMX frame, so unless it's steel and you're willing to spend $150 to have some brazed on, you're out of luck there. also, you're going to have to get a 20" (or whatever size) wheel built around an IGH hub, and finding a BMX rim to match up with IGH spoke numbers, that's going to be hard and pricey.

BMX bikes don't have fender mounts, so you're going to have to get creative and they'll also look crappy.

get yourself a freaking folder and save yourself the around $500 and tons of annoyance to convert a BMX bike into a crappy folder than doesn't fold.

Originally Posted by caloso

I learned this the hard way. They say that experience is the best teacher, but I would have been preferred to just read about it on the internet.

On my 3 Speed, all the cable mounts are clamp on. I will have to make sure I can get something that will work for this though. The SA 8-Speed has gear 1 as direct drive, so I won't have problems with getting high enough gearing. Looking online, I found rims that match the hub easily. The fenders and rack might be a challenge though.

Edit: They make 22.2mm seatposts 450mm long, could I get a lot of shims and use that?

You have a road bike avitar. Measure from the top of your saddle to the bottom extended crank. That'll help you to figure out how much seatpost you need. 450 mm is about 18". You need about 4" inside your seat tube so that's only a little more than 12" of exposed seatpost. I kind of doubt that'll be enough.

Ok, lets see:
Road Bike:87cm
Mountain bike: 84cm
3-speed: 88cm
BMX Currently: 67cm
Right now the BMX has a 200mm seatpost at the minimum insertion line(3" in). If I put the 450mm seatpost 4" in, that's about 225mm gain in length. Looks like enough to work. Any problems that could result from shimming 22.2 to 28.6? I might be able to make the shim using the existing seatpost.

OK I'm equally nuts, because I've had similar thoughts of taking a BMX frame and lacing one of the upcoming S2C kickback 2-speed hubs with a coaster brake to the 20 inch rear rim. I'm dreaming, but being kid sized myself it might be doable (with $$) and make a fun little bike for the neighborhood.

I'm having a hard time deciding on which hub to go with... SA 8 speed sounds like it was made for a project like this, but doesn't sound like it's the most reliable. Nexus 8 sounds more reliable, but is expensive and will probably add more difficulties with hub spacing and gearing. 3 Speeds are reliable and cheap, but don't quite have the gearing I want. If the roads are clear enough this weekend I should try a ride out on some hills with my 3-speed to see how bad it is.

I'm having a hard time deciding on which hub to go with... SA 8 speed sounds like it was made for a project like this, but doesn't sound like it's the most reliable. Nexus 8 sounds more reliable, but is expensive and will probably add more difficulties with hub spacing and gearing. 3 Speeds are reliable and cheap, but don't quite have the gearing I want. If the roads are clear enough this weekend I should try a ride out on some hills with my 3-speed to see how bad it is.

Yes, running a Nexus 8 on a 20 inch wheel is going to result in a whole bunch of really low gears crammed into a narrow range, unless you can come up with a monster chainwheel up front. I'd choose a 3 speed with as wide a ratio as possible. Sturmey Archer is coming out with some cool hubs.